Openvpn serving IPv6 to clients via ipv4?

Question

openvpn

Good time of the day!
There is a VPS, the Openvpn server is running on it, everything works fine using the ipv4 protocol. The server listens on the address 95.216.xxx.xxx. The VPS also has a 2a01:4f9:2a:28a7:b4::/80 IP6 address grid.
The task was to distribute the inet6 available on the VPS to clients via openvpn (of course, they do not have a native one )
.
all available network to clients)
push "route-ipv6 2000::/3"
push "dhcp-option DNS 2001:4860:4860::8888"
#----
I don't change anything in client configs. After connecting, clients receive ipv6 addresses, but of course they have no connection via inet6. I'm trying to translate addresses on the server through iptables:
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iptables -t nat -A POSTROUTING -s 2a01:4f9:2a:28a7:b4::/80 -o venet0 -j SNAT --to-source 95.216.xxx.xxx
gives error: iptables v1.4.21: invalid mask `80 ' specified. Like, she doesn't like the /80 mask :)
It also doesn't pass through ip6tables - it doesn't contain the nat table at all.
Where am I wrong? How to make this VPN work?